A hydrostatic transmission may be used in a heavy machine, such as a construction or agricultural machine, to deliver power from a power source, such as the engine, to the drivetrain of the heavy machine. The hydrostatic transmission may include one or more variators, each including a hydraulic motor paired with a hydraulic pump. The variators may be configured so as to provide continuously variable torque and speed to the drivetrain of the heavy machine, thus allowing the power source to operate at its ideal operating mode (e.g., an optimal range of revolutions per minute (RPM) or at an optimal fuel consumption rate) according to present power requirements.
One potential drawback of hydrostatic transmissions is that it has proven difficult to scale up the system, particularly with regard to the size of the hydraulic pumps and motors, to account for larger machine sizes. For example, larger displacement hydraulic pumps and motors inherently possess much more limited operating speed capabilities than smaller pumps and motors. In addition, large-sized piston hydraulic displacement pumps or motors tend to be less efficient than their smaller-sized counterparts. Further, larger-sized actuators will be required for controlling larger pumps and motors, thus requiring larger control valves to handle the higher control flow requirements and complicating the system design.
One method of addressing the aforementioned drawbacks relating to scaling difficulties is to include two or more variators operating in parallel. In such hydrostatic transmissions, however, the two variators must perform the same function (i.e., produce identical power flows) or else suffer inefficiencies caused by a mismatch in function.
U.S. Pat. No. 8,500,587 to Du et al. (the '587 patent) provides one solution that allegedly addresses the problem of matching the functions of the two parallel variators. The '587 patent discloses a hydrostatic transmission containing two variators, each comprising a hydraulic motor and hydraulic pump in a respective hydraulic circuit. To match the functions of the two variators, the two variators are connected by two bridging hydraulic links. The first bridging hydraulic link connects a first side of the hydraulic circuit of the first variator to a respective first side of the hydraulic circuit of the second variator. Similarly, the second bridging hydraulic link connects a second side of the hydraulic circuit of the first variator to a respective second side of the hydraulic circuit of the second variator. The two bridging hydraulic links may compensate for any flow difference between the hydraulic circuits of the two variators. Although the '587 patent discloses one technique for matching the functions of parallel variators, other systems and methods may be implemented to facilitate matching the functions of parallel variators.